1. Field of the Invention
The present invention relates to a resist processing method and a resist processing apparatus for forming a desired resist pattern on the surface of a substrate, such as a semiconductor wafer or an LCD substrate.
2. Description of the Related Art
For instance, in a photolithography process of manufacturing a semiconductor device, the surface of a semiconductor wafer (referred to as a xe2x80x98waferxe2x80x99 hereinafter) is first coated with a resist. And after exposing the wafer coated with a resist, the wafer is then developed.
Conventionally, as publicly known by the Japanese Patent Publication No. Hei 2-30194, these resist coating and developing processes are performed according to a predetermined sequence before and after an exposing process, within a complex processing system equipped with each corresponding processing units in one system.
However, recently, the resist pattern formed upon the wafer is required to be finer, and a severe control upon the line width of the resist pattern has become inevitable.
Such control concerning the line width of the resist pattern is now carried out, for example, by a worker measuring the actual line width of the resist pattern on the surface of the wafer brought out from the resist coating and developing system, with an SEM (Scanning Electron Microscope), and judging whether the measured value of the line width satisfies the required standards.
However, the above-mentioned method has some problems. An expensive SEM is needed and considerable labor and time is required for the measurement of the line width. Furthermore, when measuring the line width with an SEM, the wafer must once be brought out and into a vacuum testing room of the SEM, causing contamination of the wafer.
So, for example, by strictly fixing the formation conditions (conditions for coating, exposing and developing the resist) of the resist pattern, the line width of the resist pattern may be controlled more strictly, making such measurement needless. However, the inventors think that there is a limit to controlling the line width of the resist pattern in such a way, no matter how strictly the formation conditions of the resist pattern may be set.
The object of the present invention is to provide a resist processing method and apparatus enabling a highly fine control upon the line width of the resist pattern.
To solve the above-mentioned problems, a first aspect of the invention is a method for forming a predetermined resist pattern on the surface of a substrate coated with an undercoat, comprising the steps of (a) detecting a light reflectivity of the undercoat, (b) coating the substrate with a resist, based upon a first condition, (c) exposing the substrate already coated with the resist, based upon a second condition, (d) developing the exposed substrate, based upon a third condition and (e) controlling at least one of the first, second and third conditions, based upon the detected reflectivity.
A second aspect of the invention is an apparatus for forming a predetermined resist pattern on a substrate already coated with an undercoat, comprising means for detecting a light reflectivity of the undercoat; means for coating the resist on the substrate based upon a first condition; means for exposing the substrate coated with the resist based upon a second condition; means for developing the exposed substrate based upon a third condition; and means for controlling at least one of the first, second and third conditions based upon the detected reflectivity.
When exposing the substrate coated with a resist, light reflects on the undercoat formed under the resist, and this reflected light also helps exposure. Therefore, when the reflectivity of the undercoat differs, the exposure level differs, changing the line width of the resist pattern.
On the other hand, for example, SiO2 and Al having different light reflectivity are formed as the undercoat upon a semiconductor wafer as a substrate. Corresponding to the circuit pattern to be formed, the ratio between the area of SiO2 and the area of A1 differs, changing the light reflectivity of the undercoat according to the ratio. When the resist pattern is formed under the same conditions, the line width of the resist pattern changes according to the light reflectivity of the undercoat. The present invention first detects the light reflectivity of the undercoat. And based on the detected reflectivity, the invention controls these conditions, enabling a highly fine control upon the line width of the resist pattern.
A third aspect of the invention is a method for forming a predetermined resist pattern on a substrate already coated with a predetermined undercoat, by coating a resist, exposing and developing, comprising the steps of (a) forming said predetermined undercoat on a substrate for measurement, along with the substrate, (b) coating a resist on the measurement substrate, (c) exposing the measurement substrate, to find out the exposure energy needed and sufficient for the resist to be fully exposed and (d) performing a predetermined process, based upon the exposure energy determined.
These and other objects and profits of the invention can be easily defined by the following explanations and the accompanying drawings.